Tektronix 2465BCT Test 05 Fail 44 (24) Troubleshooting (issue solved)

[peter-h]

I will do, KCT99. Many thanks for your info.

[Antonionavan]

Please, can you help me with my tektronix 2465, i have a similar issue, i repair some bad connections but no work yet. I am at the same point than you was before fix the resistor connection.

[Antonionavan]

Please, can you help me with my tektronix 2465, i have a similar issue, i repair some bad connections but no work yet. I am at the same point than you was before fix the resistor connection. You can give me the DAC Voltages?

[peter-h]

KCT_99

I have bought another old scope (2465DVS) and been working on this 2465B.

I checked the DAC is generating the right "cloud" and the two 4051 demuxes after it are working right. The various front panel knobs come through as varying voltages.

Traving the A TRIG LVL and B TRIG LVL voltages, I see A TRIG LVL and B TRIG LVL go all the way through to U500 TLA. Twiddling the trig level knob, with and without pressing the A/B switch, produces -1V to +1V on these two signals.

I have not checked the U500 pins themselves, which are accessible only on the back of the PCB.

This is a very clean 2465B, late model, year 1994 date codes.

So this looks like bad news and U500 may be duff.

The -1.25V and +1.36V rails are good.

I have ordered a U500 chip from a firm on Ebay and will report the result.

[peter-h]

The replacement U500 module fixed the problem.

Quite inexpensive, from a company on the island of Rhodes in Greece Nice people; they have loads of these

https://www.ebay.co.uk/itm/TEKTRONIX-Hybrid-IC-155-0239-01-A-B-Trigger-U500-2400-Series-Oscilloscopes/382200577959

qservice_rhodes

Took all of 5 mins to replace it.

One of the two chips under the ceramic cover:



Somebody mentioned that there was a possibility of a 3rd party module but I can't see how unless Tek publish a circuit diagram, and anyway this is probably a custom chip.

[siggi]

Somebody mentioned that there was a possibility of a 3rd party module but I can't see how unless Tek publish a circuit diagram, and anyway this is probably a custom chip.

There exists at least a data sheet for the die. See 203-0213-90 on page 6-43 in this document http://w140.com/tek_made_sm.pdf. I seem to remember reasoning out that each hybrid contains two of those, though I forget the details.

[peter-h]

Very interesting!

I photographed both chips and on close inspection they look the same.

Yes one could do a design based on that data.

The power consumption numbers explain the heat generated - of the order of 3 watts for the whole module.

[siggi]

I photographed both chips and on close inspection they look the same.

Right - I remember now.
There's one die for each of the A and B triggers, with channels 1-4 routed to the corresponding inputs on both dies. The fifth channel on each hybrid is then dedicated to "another thing". The A trigger die does line triggering, whereas the B trigger die does something weird with the 5th channel - it might be used only for power-on self tests...

[peter-h]

The other chip - 180 degrees different orientation



I broke off some bonding wires but if anybody wants this module, PM me your address.

[KCT_99]

Hi Guys,

I apologize, I was offline for a while and side tracked with things in my crawl space. I also had another 2465BCT on my plate. Guess what same issue as I described on my first post on this thread altho no trace was gummed away, so I got it just in time. This capacitor issue seems quite nagging and I would suspect this been an issue even with newer vintage models. For good measure I replaced the NVRAM Chip as well since I had it all apart. I took a few more pictures on this job for you guys.

Also, I attached the NVRAM data below as ZIP file in case this might be useful for someone.

[peter-h]

That is weird. Where did that messy stuff covering the 1206 resistors come from? It doesn't look like it leaked from those capacitors, and anyway those are modern reflow solderable caps which last for decades.

[KCT_99]

Hi Peter,
yes, these fine electrolytic capacitors leak and gum up this area covering the 1206s with crap and potentially eating the traces away even under the solder mask. I suspect these capacitors are underrated and perhaps of low quality. I replaced them with higher voltage rated and lower ESR rated capacitors.

This is the brutal but effective way to deal with this. 

https://youtu.be/X8N9O3a9jiM

[peter-h]

Yes; these components could be from 30+ years ago and capacitors were different then. If you tried to lead-free solder these, they would "pop" due to the extra temperature. But also these were really early days of SMT.